Polymer blends are known in the prior art. However, the prior art polymer blends are generally lacking in one or more properties necessary for use as a food or beverage packaging material. Such properties include tensile and impact strength, rigidity, gas permeation resistance, and low cost.
Hallden-Abberton et al U.S. Pat. No. 4,727,117 discloses glutarimide polymers suitable for blending with other thermoplastic materials. The patent discloses blends of the claimed polyglutarimides with polycarbonates; polycarbonate-multistage polymer blends; styrene-acrylonitrile copolymers and blends; and several other polymers. However, the patent does not suggest the three-component polymer blend claimed herein.
Various blends of polycarbonates with styrene-acrylonitrile copolymers are disclosed in Van Bokhoven et al U.S. Pat. No. 4,560,725 and Serini et al U.S. Pat. No. 4,564,654. These polymer blends do not possess adequate resistance to oxygen and carbon dioxide permeation for use as a food packaging material. Other polymer blends containing a high proportion of polycarbonate also generally lack gas permeation resistance.
It is a principal objective of the present invention to provide a polymer blend comprising a polycarbonate, an acrylonitrile-methyl acrylate copolymer, and an imide-acrylate copolymer containing acidic or anhydride groups which have been alkylated or esterified.
A related objective of the present invention is to provide a polymer blend having an adequate combination of tensile strength, rigidity, gas permeation resistance, and low cost for consideration as a food or beverage packaging material.
Additional objectives and advantages of the invention will become apparent to persons skilled in the art from the following detailed description.